The present invention is in the field of automated material handling for exposure systems. More particularly, the present invention provides for a method and apparatus for automatic removal of slip sheets which have been interleaved with imaging plates without the use of any physical contact between the removal mechanism and the slip sheets.
Printing processes utilize a vast array of different technologies to transfer written content to various distribution media. One way in which content is transferred is by computer to plate (CTP) systems. The CTP process eliminates film as an intermediate transfer mechanism and allows the optical exposure of the plate directly. This reduces the number of steps required in the printing process and potentially eliminates the cost associated with the generation of the intermediate film and its handling.
In simple terms, a CTP system accepts jobs written in a page description language. These jobs are controlled through execution by priority and scheduling workflow software. Jobs are then sent through a raster image processor where the data is transformed into a raster format for printing by a digital platemaker. The platemaker system takes this data and prints it on a photosensitive coated medium, typically a sheet of aluminum coated with a photosensitive polymer, which is later notched, bent, hung on the press, inked and made ready to print on paper.
Also included in the automation of a CTP system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker system and it is desirable to reduce the amount of operator handling involved. In CTP systems, the printing plates to be exposed possess a photosensitive coating on one side that can degrade upon prolonged exposure to a normal atmosphere and ambient light levels. Also, the photosensitive surface of the plate, typically a photopolymer, can react with the uncoated metallic side of the plate immediately above it when placed in a stack of plates. Most manufacturers of these types of printing plates attempt to minimize this surface-to-surface interaction and other degradation problems by interleaving an inert slip sheet between each printing plate. The slip sheets are sometimes coated.
These slip sheets must be removed in order for a robotic or automated system to be able to automatically load one plate at a time onto the exposure system. If the slip sheet is not removed effectively and efficiently, the slip sheets may become entangled in the system preventing plates from being transported through the system of being exposed properly and the machine and any subsequent plate development processors may jam or cease functioning.
There have been a number of previous attempts to develop effective slip sheet removal systems. In general, mechanical methods are used to physically contact the slip sheet, either with suction cups or other means of physical attachment. Prior slip sheet removal attempts have involved at least some contact between a mechanical device and the slip sheet. Because of the mechanical interaction with the slip sheet, there are many precise timing issues that must be coordinated. For instance, the slip sheet xe2x80x9cpickerxe2x80x9d must be coordinated to interact with the plate picker so as not to interfere with it. Further, the slip sheet picker must have a method of locating the slip sheet, probably through some sort of slip sheet detection device. There is a need to precisely determine the location of the slip sheet and to make sure the slip sheet is in the correct place.
The present invention does not require any physical contact with a slip sheet. Instead, the invention uses directed gas flow to remove and discard the slip sheet into a discarded slip sheet holding bin.
The present invention provides various methods and apparatus for material handling in a context where lightweight sheets to be discarded are interleaved between heavier items to be further processed, such as in separating slip sheets that are interleaved with imaging plates. For example, the present invention provides a unique slip sheet removal system by using gas, preferably air, delivered by nozzles to direct slip sheets into a discarded slip sheet holding area or bin. More specifically, in a preferred embodiment, the invention provides for a slip sheet removal system that involves pulsing air jets which create a layer of air between the slip sheets and the plates and then directs the exposed slip sheet on the stack of plates to the holding bin. The invention also provides for an apparatus for the slip sheet removal system. More specifically, in a preferred embodiment, the invention provides for a media cart which comprises a plate handling area and a discarded slip sheet holding bin and a moving head which comprises vacuum cups, air nozzles, a baffle and other parts used to move plates from a stack to the recording area.